MRA is a widely performed clinical diagnostic procedure and is rapidly replacing x-ray based methods of angiography. If the speed with which MRA data could be increased, then clinical utility would be extended to include time resolved angiograms that could be used to make additional diagnoses.
Currently, three-dimensional angiography acquisitions take about 30 seconds to complete. During this time, a bolus injection of contrast agent has to be imaged as it passes through the vascular system. In an attempt to capture the contrast as it first enters the arterial system, commercial scanners use “centric coding”. In this process, the central regions of the three-dimensional data acquisition are acquired first, followed by the outer regions of the three-dimensional data set. This approach helps capture the early contrast conditions but the disadvantage is that it still requires acquisition of the full three-dimensional data set to complete the scan. Another approach is only to acquire the central data of the three-dimensional data set (in the k-space domain), and while this rapidly captures the contrast conditions, the resolution of the data set is reduced. The centric approaches can reduce the scan time by about 75%. A third technique uses an approach developed by the inventor, to distribute the acquisition of spatial data in such a manner as to sparsely sample data and use interpolation of the time dimension to retrospectively fill in the data. The disadvantage of this technique is that it is very susceptible to breathing motion, which causes artifact.
The present invention uses a data mask to guide the acquisition of three-dimensional data. The advantage of this approach is that it allows data to be acquired to capture contrast information with high-resolution detail. The acquisition requires rapidly acquiring a two-dimensional data set and processing this data by thresholding to guide the subsequent three-dimensional data set. The additional processing requires an additional step in the scanner.